1. Field of the Invention
The present invention relates to a driving apparatus for a bicycle and, more specifically, to a speed changer using speed change means formed by combination of a pair of non-circular gears.
2. Description of Related Art
A conventionally widely used driving apparatus with a speed changer for a bicycle interposes an external speed changer between a crank sprocket and a rear wheel side sprocket. The external speed changer comprises a plurality of sprockets differing in number of teeth and concentrically fixed to be disposed at a crank gear or a rear freewheel so that a derailler shifts a driving chain axially with respect to the free-wheel to engage the chain with a different sprocket, thereby varying an angular velocity ratio.
Such driving apparatus with the speed changer has the problem in that the angular velocity ratio only changes stepwise and the speed change may not be smooth when subjected to a large torque.